A. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same. Particularly, it relates to a semiconductor device mounted with power semiconductor elements etc. and a method for manufacturing the semiconductor device.
B. Description of the Related Art
An example of a semiconductor device in which semiconductor elements are modularized has a package structure shown in FIG. 9. In the semiconductor device shown in FIG. 9, cooling plate 51 is arranged in a bottom portion of resin casing 52. Insulating wiring board 56 is arranged on cooling plate 51. Insulating wiring board 56 is configured in such a manner that metal layers 54 and 55 are bonded to opposite surfaces of insulating substrate 53. Metal layer 55 of insulating wiring board 56 and cooling plate 51 are bonded to each other through solder layer 57a. Semiconductor elements 58 are arranged on insulating wiring board 56. Metal layer 54 of insulating wiring board 56 and semiconductor elements 58 are bonded to each other through solder layer 57b. In addition, external terminals 59 are arranged on insulating wiring board 56. Metal layer 54 of insulating wiring board 56 and external terminals 59 are bonded to each other through solder layer 57c. Semiconductor elements 58 are electrically connected to external terminals 59 respectively by bonding wires 60. The inside of resin casing 52 is filled and sealed with sealing resin 61.
High heat dissipation is required particularly in the case of semiconductor elements which generate significant heat, like power semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistor) etc. However, in such a semiconductor device according to the background art, bonding wires 60, for example, consisting of thin aluminum wires each having a wire diameter of about 300 μm to 400 μm are only connected to the upper surface sides of semiconductor elements 58. Moreover, since heat is generated in accordance with electricity passing through bonding wires 60, it is almost impossible to obtain any heat dissipation effect from the upper surface sides of semiconductor elements 58.
A method for improving wiring current density, fusing current resistance, bonding reliability, heat dissipation, etc. has been described in PTL 1 and PTL 2. In PTL 1 and PTL 2, an implant board and semiconductor elements of a semiconductor mounting board are bonded to each other through implant pins in place of the wire bonding wiring structure.
A semiconductor device disclosed in PTL 1 will be described with reference to FIGS. 10 and 11. Incidentally, portions substantially the same as those in the semiconductor device shown in FIG. 9 are referred to by corresponding numerals, so that description thereof will be omitted.
In the semiconductor device shown in FIG. 10, semiconductor elements 58 are arranged on insulating wiring board 56. Metal layer 54 of insulating wiring board 56 and semiconductor elements 58 are bonded to each other through solder layer 57b. 
Implant board 79 is arranged above semiconductor elements 58. Implant board 79 and semiconductor elements 58 are electrically connected to each other through implant pins 76 of implant board 79.
Implant board 79 includes insulating wiring board 75, and implant pins 76 press-fitted into via holes 74. Insulating wiring board 75 is configured in such a manner that metal layers 72 and 73 forming a printed wiring are bonded to opposite surfaces of insulating substrate 71. Via holes 74 are formed to penetrate insulating substrate 71, metal layer 72 and metal layer 73 of insulating wiring board 75. Referring now to FIG. 11, collar portion 77 is provided in each implant pin 76. A constant quantity between one end of the implant pin and collar portion 77 is press-fitted into via hole 74. Collar portion 77 and insulating wiring board 75 are bonded to each other through bonding material 78a. Moreover, the other end of implant pin 76 is bonded to insulating wiring board 56 or semiconductor element 58 through bonding material 78b     PTL 1: JP-A-2011-82303    PTL 2: WO 2011/083737